1. Field of the Invention
The present invention relates to a prime focus unit, and more particularly, to a prime focus unit suitable for use as an apparatus for effecting observation at the prime focus of a large telescope.
2. Description of the Background Art
FIG. 6 is a conceptual diagram for describing the structure of an optical system of a telescope. Reference numeral 1 designates a primary mirror; 2 designates a secondary mirror; and 3 designates a tertiary mirror. Further, reference numeral 4 designates a prime focus; 5 designates a Cassegrain focus; and 6 designates a Nasmyth focus.
The primary mirror 1 reflects light originating from stars and entering a telescope. In a case where the secondary mirror 2 is not provided, the light reflected from the primary mirror 1 forms an image at the prime focus 4. In a case where the secondary mirror 2 is provided, the light reflected from the primary mirror 1 is reflected by the secondary mirror 2 before forming an image at the prime focus. The secondary mirror 2 is disposed such that the light reflected from the secondary mirror 2 forms an image at a predetermined point behind the telescope. The predetermined point; that is, a point at which the light reflected from the secondary mirror 2 forms an image, corresponds to the Cassegrain focus. In a case where the tertiary mirror 3 is disposed, the axis of the light reflected from the secondary mirror 2 is bent at 90xc2x0 by the tertiary mirror 3. The Nasmyth focus 6 corresponds to a point at which the light whose axis is bent forms an image to the side of the telescope.
In a case where an observation apparatus for observing light originating from stars is disposed at the prime focus 4, the light originating from stars is shielded by the observation apparatus, thus raising a problem of substantially diminishing the effective aperture of the telescope. To prevent such a problem, the observation apparatus is usually disposed at the Cassegrain focus 5 or at the Nasmyth focus 6.
However, in the case of the large telescope, a decrease in the effective aperture of the telescope, which would be caused by the observation apparatus being disposed at the prime focus 4, can be substantially ignored. In a case where the observation apparatus is disposed at the prime focus 4, a wider view angle of observation can be ensured as compared with the case where the observation apparatus is disposed at the Cassegrain focus 5 or at the Nasmyth focus 6. Thus, a configuration in which an observation apparatus is disposed at the prime focus 4 can be considered a practical configuration for a large telescope.
In a conceivable configuration of a large telescope in which an observation apparatus is disposed at the prime focus 4, the observation apparatus is fixed within a lens barrel of the telescope through use of; for example, members possessing rigidity. The attitude of the lens barrel is changed according to the position of a star that is an object of observation. If the observation apparatus is fixed within the lens barrel, the direction in which the weight of the observation apparatus acts on the lens barrel is changed according to the attitude of the lens barrel.
If the direction in which the weight of the observation apparatus acts on the lens barrel is changed, deformation corresponding to the change arises in the rigid members and the lens barrel that retain the observation apparatus. In the event of a change in the position or angle of the observation apparatus, observation conditions of the observation apparatus are also changed. Accordingly, depending on the structure for fixing the observation apparatus within the lens barrel, light originating from stars cannot be stably and accurately observed at all times.
The present invention has been conceived to solve the foregoing drawback in the background art and is aimed at providing a prime focus unit which enables position and angle correction within a lens barrel, as required, while being located at the prime focus of a telescope.
The above objects of the present invention are achieved by a prime focus unit for collecting observation data at the prime focus of a telescope. The unit includes a first frame fixed on the telescope. The unit also includes an observation apparatus for collecting the observation data. A second frame is provided so that the observation apparatus is to be mounted thereon. An adjustment mechanism is interposed between the first and second frames so as to adjust the relative position and angle therebetween.